PTHREAD_ATTR_INIT(3)      Linux Programmer's Manual     PTHREAD_ATTR_INIT(3)

NAME         top

       pthread_attr_init,  pthread_attr_destroy  -  initialize  and  destroy
       thread attributes object

SYNOPSIS         top

       #include <pthread.h>

       int pthread_attr_init(pthread_attr_t *attr);
       int pthread_attr_destroy(pthread_attr_t *attr);

       Compile and link with -pthread.

DESCRIPTION         top

       The pthread_attr_init() function initializes the thread attributes
       object pointed to by attr with default attribute values.  After this
       call, individual attributes of the object can be set using various
       related functions (listed under SEE ALSO), and then the object can be
       used in one or more pthread_create(3) calls that create threads.

       Calling pthread_attr_init() on a thread attributes object that has
       already been initialized results in undefined behavior.

       When a thread attributes object is no longer required, it should be
       destroyed using the pthread_attr_destroy() function.  Destroying a
       thread attributes object has no effect on threads that were created
       using that object.

       Once a thread attributes object has been destroyed, it can be
       reinitialized using pthread_attr_init().  Any other use of a
       destroyed thread attributes object has undefined results.

RETURN VALUE         top

       On success, these functions return 0; on error, they return a nonzero
       error number.

ERRORS         top

       POSIX.1 documents an ENOMEM error for pthread_attr_init(); on Linux
       these functions always succeed (but portable and future-proof
       applications should nevertheless handle a possible error return).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface              Attribute     Value   │
       │pthread_attr_init(),   │ Thread safety │ MT-Safe │
       │pthread_attr_destroy() │               │         │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       The pthread_attr_t type should be treated as opaque: any access to
       the object other than via pthreads functions is nonportable and
       produces undefined results.

EXAMPLE         top

       The program below optionally makes use of pthread_attr_init() and
       various related functions to initialize a thread attributes object
       that is used to create a single thread.  Once created, the thread
       uses the pthread_getattr_np(3) function (a nonstandard GNU extension)
       to retrieve the thread's attributes, and then displays those

       If the program is run with no command-line argument, then it passes
       NULL as the attr argument of pthread_create(3), so that the thread is
       created with default attributes.  Running the program on Linux/x86-32
       with the NPTL threading implementation, we see the following:

           $ ulimit -s       # No stack limit ==> default stack size is 2MB
           $ ./a.out
           Thread attributes:
                   Detach state        = PTHREAD_CREATE_JOINABLE
                   Scope               = PTHREAD_SCOPE_SYSTEM
                   Inherit scheduler   = PTHREAD_INHERIT_SCHED
                   Scheduling policy   = SCHED_OTHER
                   Scheduling priority = 0
                   Guard size          = 4096 bytes
                   Stack address       = 0x40196000
                   Stack size          = 0x201000 bytes

       When we supply a stack size as a command-line argument, the program
       initializes a thread attributes object, sets various attributes in
       that object, and passes a pointer to the object in the call to
       pthread_create(3).  Running the program on Linux/x86-32 with the NPTL
       threading implementation, we see the following:

           $ ./a.out 0x3000000
           posix_memalign() allocated at 0x40197000
           Thread attributes:
                   Detach state        = PTHREAD_CREATE_DETACHED
                   Scope               = PTHREAD_SCOPE_SYSTEM
                   Inherit scheduler   = PTHREAD_EXPLICIT_SCHED
                   Scheduling policy   = SCHED_OTHER
                   Scheduling priority = 0
                   Guard size          = 0 bytes
                   Stack address       = 0x40197000
                   Stack size          = 0x3000000 bytes

   Program source

       #define _GNU_SOURCE     /* To get pthread_getattr_np() declaration */
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
               do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       static void
       display_pthread_attr(pthread_attr_t *attr, char *prefix)
           int s, i;
           size_t v;
           void *stkaddr;
           struct sched_param sp;

           s = pthread_attr_getdetachstate(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getdetachstate");
           printf("%sDetach state        = %s\n", prefix,

           s = pthread_attr_getscope(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getscope");
           printf("%sScope               = %s\n", prefix,
                   (i == PTHREAD_SCOPE_SYSTEM)  ? "PTHREAD_SCOPE_SYSTEM" :

           s = pthread_attr_getinheritsched(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getinheritsched");
           printf("%sInherit scheduler   = %s\n", prefix,
                   (i == PTHREAD_INHERIT_SCHED)  ? "PTHREAD_INHERIT_SCHED" :

           s = pthread_attr_getschedpolicy(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getschedpolicy");
           printf("%sScheduling policy   = %s\n", prefix,
                   (i == SCHED_OTHER) ? "SCHED_OTHER" :
                   (i == SCHED_FIFO)  ? "SCHED_FIFO" :
                   (i == SCHED_RR)    ? "SCHED_RR" :

           s = pthread_attr_getschedparam(attr, &sp);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getschedparam");
           printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

           s = pthread_attr_getguardsize(attr, &v);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getguardsize");
           printf("%sGuard size          = %d bytes\n", prefix, v);

           s = pthread_attr_getstack(attr, &stkaddr, &v);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getstack");
           printf("%sStack address       = %p\n", prefix, stkaddr);
           printf("%sStack size          = 0x%zx bytes\n", prefix, v);

       static void *
       thread_start(void *arg)
           int s;
           pthread_attr_t gattr;

           /* pthread_getattr_np() is a non-standard GNU extension that
              retrieves the attributes of the thread specified in its
              first argument */

           s = pthread_getattr_np(pthread_self(), &gattr);
           if (s != 0)
               handle_error_en(s, "pthread_getattr_np");

           printf("Thread attributes:\n");
           display_pthread_attr(&gattr, "\t");

           exit(EXIT_SUCCESS);         /* Terminate all threads */

       main(int argc, char *argv[])
           pthread_t thr;
           pthread_attr_t attr;
           pthread_attr_t *attrp;      /* NULL or &attr */
           int s;

           attrp = NULL;

           /* If a command-line argument was supplied, use it to set the
              stack-size attribute and set a few other thread attributes,
              and set attrp pointing to thread attributes object */

           if (argc > 1) {
               int stack_size;
               void *sp;

               attrp = &attr;

               s = pthread_attr_init(&attr);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_init");

               s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setdetachstate");

               s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setinheritsched");

               stack_size = strtoul(argv[1], NULL, 0);

               s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
               if (s != 0)
                   handle_error_en(s, "posix_memalign");

               printf("posix_memalign() allocated at %p\n", sp);

               s = pthread_attr_setstack(&attr, sp, stack_size);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setstack");

           s = pthread_create(&thr, attrp, &thread_start, NULL);
           if (s != 0)
               handle_error_en(s, "pthread_create");

           if (attrp != NULL) {
               s = pthread_attr_destroy(attrp);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_destroy");

           pause();    /* Terminates when other thread calls exit() */

SEE ALSO         top

       pthread_attr_setaffinity_np(3), pthread_attr_setdetachstate(3),
       pthread_attr_setguardsize(3), pthread_attr_setinheritsched(3),
       pthread_attr_setschedparam(3), pthread_attr_setschedpolicy(3),
       pthread_attr_setscope(3), pthread_attr_setstack(3),
       pthread_attr_setstackaddr(3), pthread_attr_setstacksize(3),
       pthread_create(3), pthread_getattr_np(3), pthreads(7)

COLOPHON         top

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Linux                            2015-07-23             PTHREAD_ATTR_INIT(3)